1. Field of the Invention
The present invention relates in general to a fan protection device, more particularly to a protection device to protect a fan from overpowering and overheating.
2. Description of the Related Art
Conventional fan protection devices are activated to allow the fans to be shut down when blockage or stalling of the fan is caused by obstacles or less obvious reasons. Fatigue in fan-shafts is unavoidable due to constant use, added to the increase in friction, resulting in heat generation and larger driving current. Thus fans may constantly overheat or overload with large current. Either case will increase the likelihood of fans igniting. This not only damages the fans, but also imposes a greater danger on the systems cooled by the fans. Moreover, when fans are obstructed by obstacles, they may not come to a complete halt, and the continued rotation requires increased current to sustain. When there is no device in conventional fan protection devices to detect such a situation, this kind of damage occurs easily, shortening the life span of the fan and posing great danger to its environment.
An object of the present invention is to provide a fan protection device as shown in FIG. 1, comprising: a temperature detector 10, a current detector 12 and an alarm unit 14. The temperature detector 10 is used to detect overheating of the fan. The temperature detector 10 comprises a temperature-voltage transformer 10a and an overheating-judgment device 10b. The temperature-voltage transformer 10a is located at the thermo-generating source of the fan, to transform the thermo-energy thereof into a corresponding voltage signal Vt; and the overheating-judgment device 10b is used to determine whether the fan temperature exceeds a predetermined temperature according to an output voltage signal Vt from the temperature-voltage transformer 10a and then deciding whether the fan is overheated.
The current detector 12 is used for detecting overload of driving current of the fan. The current detector 12 comprises a current-voltage transformer 12a and an overload-judgment device 12b. The current-voltage transformer 12a is located on the path of the current flow of the fan, for transforming the current of the fan into a corresponding voltage signal Vi; and the overload-judgment device 12b is used to determine whether the current of the fan surpasses a predetermined current according to the current-voltage transformer 12a and deciding whether the fan is overloaded.
The alarm unit 14 may function as a lockup device. When the fan is operating normally, the lockup device sends a signal V0 of a first state to keep the switch SW conductive, and allows the fan to maintain normal operations. If one of the overheating and overload of the fan is detected, the lockup device outputs a signal of a second state to cut off the power supply to the fan to stop the fan from operating, until the lockup device is reset.